A redox flow battery (RF battery) is one of large-capacity storage batteries storing electric power generated by means of renewable energy power generation such as solar photovoltaic power generation and wind power generation. The RF battery is a battery charged and discharged by utilizing the difference in oxidation-reduction potential between an ion contained in a positive electrode electrolyte and an ion contained in a negative electrode electrolyte. FIG. 9 illustrates the principle of operation of a conventional RF battery 300 containing a vanadium ion as its ion.
As shown in FIG. 9, RF battery 300 includes a cell 100 in which a positive electrode cell 102 and a negative electrode cell 103 are separated from each other by an ion exchange film 101 through which hydrogen ions are transmitted. Positive electrode cell 102 includes a positive electrode 104 therein, and is connected via pipes 108 and 110 to a positive electrode electrolyte tank 106 storing a positive electrode electrolyte. Negative electrode cell 103 includes a negative electrode 105 therein, and is connected via pipes 109 and 111 to a negative electrode electrolyte tank 107 storing a negative electrode electrolyte. The electrolytes stored in tanks 106 and 107 are circulated through cells 102 and 103 by pumps 112 and 113, respectively.
RF battery 300 usually utilizes a structure referred to as a cell stack including a plurality of stacked cells 100 (see Patent Document 1 (Japanese Patent Laying-Open No. 2002-237323) and Patent Document 2 (Japanese Patent Laying-Open No. 2004-319341), for example). FIG. 10 is a schematic structural diagram of a conventional cell stack. A cell stack 200 is formed by repeatedly stacking a cell frame 120 having a bipolar plate 121 integrated with a frame body 122, positive electrode 104, ion exchange film 101, and negative electrode 105 in this order, and sandwiching and clamping the stack between two end plates 210 and 220.
In cell stack 200, one cell is formed between adjacent cell frames 120. In cell stack 200, the electrolytes pass through a positive electrode liquid supply manifold 123, a negative electrode liquid supply manifold 124, a positive electrode liquid discharge manifold 125, and a negative electrode liquid discharge manifold 126 that are formed in frame body 122.
Specifically, the positive electrode electrolyte is supplied from positive electrode liquid supply manifold 123 to positive electrode 104 through a slit formed on one surface side (front side in the plane of the figure) of frame body 122, and is discharged to positive electrode liquid discharge manifold 125 through a slit formed in an upper portion of frame body 122. The negative electrode electrolyte is supplied from negative electrode liquid supply manifold 124 to negative electrode 105 through a slit formed on the other surface side (rear side in the plane of the figure) of frame body 122, and is discharged to negative electrode liquid discharge manifold 126 through a slit formed in an upper portion of frame body 122.
An annular sealing member 127 such as an O ring or a flat gasket is arranged between cell frames 120, to prevent leakage of the electrolytes from between cell frames 120.